1. Field of the Invention
The present invention relates generally to the field of gas-generating devices for inflatable systems, and particularly to those used in inflatable restraint systems.
2. Background of the Invention
Prior art inflatable systems typically use an initiator (such as an electronic squib) and a booster material (such as boron potassium nitrate) to ignite a surrounding, much larger quantity of gas-generating propellant material (such as sodium azide, potassium nitrate or ammonium nitrate, and binders). The gas-generating propellant serves as the primary means by which sufficient gas is produced to deploy the inflatable system. The initiator, the booster material, and the surrounding gas-generating propellant are typically all confined within a metallic structure or assembly, the whole of which forms the “gas generator” which produces inflating gas for an inflatable component (such as an air bag in a passenger vehicle).
This gas generator assembly typically contains one or more internal chambers or baffles, as well as one or more internal sets of filters, which are designed to: (a) control the burn rate of the propellant and the gas mass flow rate, (b) reduce the temperature of the gases produced by the burning of the gas-generating material, and (c) filter out accelerated particles before the gases pass through vents in the assembly and into the airbag itself.
The gas generator is typically located in a position external to the inflatable component (e.g. an airbag) itself, and is attached to the inflatable component by a conduit through which the generated gases flow into the inflatable component, causing the inflatable component to deploy.
Such prior art systems are disclosed, for example, in U.S. Pat. No. 5,738,374 (a pyrotechnic gas generator for an air bag using an annular charge of a mixture of ammonium perchlorate and sodium nitrate, with a silicone binder); U.S. Pat. No. 5,623,115 (a gas generator including a pyrogen igniter enclosing a unitary grain of ignition material, with a squib located to ignite the unitary grain); U.S. Pat. No. 5,483,896 (a housing for a pyrotechnic inflator which serves as a filter for entrapping contaminants and as a cooler by absorbing heat from the generated gas); U.S. Pat. No. 5,443,286 (a gas generating cartridge surrounded by filtering and cooling screens); U.S. Pat. No. 4,200,615 (a linear igniter and pyrotechnic material extending longitudinally within an elongated enclosure); U.S. Pat. No. 4,950,458 (a two-stage gas generator, in which each stage includes a combustion chamber with an igniter); and U.S. Pat. No. 4,923,212 (a lightweight pyrotechnic inflator consisting of six component parts, including mechanical parts, a filter, a propellant assembly and an initiator).
Hybrid inflators such as the inflators disclosed in U.S. Pat. No. 5,670,738 (a hybrid inflator using compressed gas together with an initiator and a pyrotechnic gas generator), U.S. Pat. No. 5,660,412 (a hybrid inflator consisting of a pressure vessel containing a main charge of pyrotechnic material and a secondary charge of pyrotechnic material, wherein the secondary charge produces products of combustion that ignite the main charge), U.S. Pat. No. 5,588,676 (a hybrid inflator with a pyrotechnic gas generator and a gas chamber storing pressurized gas), U.S. Pat. No. 5,462,307 (a hybrid air bag inflator with a first chamber containing compressed gas and a second chamber containing an igniter and pyrotechnic material) and U.S. Pat. No. 5,131,680 (an inflator assembly which includes pyrotechnic material and a container of gas under pressure) also use gas generating units that are completely separate from and external to the inflatable component (e.g., the air bag) itself.
U.S. Pat. No. 6,062,143, which is assigned to the assignee of the present application and is incorporated herein by reference, discloses a distributed charge inflator. The distributed charge inflator generally includes a distributed gas-generating material, that may have a faster burning center core ignition material surrounded by supplemental propellant, or uses a homogenous mixture of ignition material and propellant, and also includes an initiator (e.g., an electronic squib) used to ignite the gas generating material upon a signal from an initiating device. The fast burning gas generating material or “distributed charge” is designed to be installed within and distributed along the interior of the undeployed inflatable component itself. It is not necessary to contain the distributed charge inflator (DCI) within any type of exterior housing or assembly. The distributed charge inflator is simpler and less expensive to manufacture than the prior art systems listed above, because it does not require the complicated series of chambers, baffles, or filters. Also, because distributed charge inflator is distributed, rather than confined to a small enclosed container as in the prior art systems listed above, it generates gases and releases the generated gases with far less explosive force than in the prior art systems. The internal distributed charge inflator system virtually eliminates the uneven inflations, pressure waves, and inertial effects of gases injected into the inflatable components from externally located gas generators. Moreover, the distributed charge inflator equipped inflatable restraints deploy less aggressively than existing systems because the energy of the expanding gases is essentially distributed uniformly throughout the inflatable structure during deployment.
Further, because the distributed charge inflator is distributed internally within the inflatable component, there is no necessity to reinforce the inflatable fabric or bladder material against pressure, heat and high velocity particulates at the point at which gases would have been forcefully injected into the inflatable component from the gas generator external to the inflatable component. Furthermore, there is no need for a reinforced fill tube, or other means for providing a secure conduit from the gas generator to the inflatable component.
An additional advantage is that it can be readily scaled to the particular application. Almost every different vehicle platform or different application requires a different volume of the inflating gas, or a different rate of inflation.
The distributed charge inflator is not limited to simply propagating the rapid ignition of other materials, the burning of which then produces the quantities of gas necessary to inflate a given structure. The distributed charge inflator system is a complete, autonomously-operating inflation system.
Example of inflatable components which the distributed charge inflator can be used to inflate are described in U.S. Pat. No. 5,282,648 (body and head restraints); U.S. Pat. No. 5,322,322 (side impact head strike protection); U.S. Pat. No. 5,480,181 (side impact head strike protection); and U.S. Pat. No. 5,464,246 (tubular cushions), which are incorporated herein by reference, as well as automotive air bags and other inflatable products.